ALANINE/ESR DOSIMETRY FOR MEASUREMENT OF ELECTRON DOSES IN INDUSTRIAL APPLICATIONS

In this report, the results of preliminary research on L-alanine/ESR electron dosimeters are described. They include the designs of modelling tools and experimental capsules, the preparation and irradiation of very thin dosimeters, the measurement of ESR signal spectrum and the calibration method. The physical, chemical and dosimetric properties of the alanine free radical dosimeters, such as the smallest thickness, average density, lowest detectable limit, repeatability of the method, reproducibility resulted in directivity and location in resonance cavity, linearity regions as well as relative scattering of the response to identical doses, are summarized.

Measurement of Electron Return Effect and Skin Dose Reduction by a Bolus in an Anthropomorphic Physical Phantom under a Magnetic Resonance Guided Linear Accelerator (MR-LINAC) System

Background: Magnetic resonance image-guided radiation therapy (MR-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board MR imaging. Under the influence of a magnetic field, however, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). The purpose of the study is to compare the exit skin dose computed by Monte Carlo dose calculation with measurements using an adult anthropomorphic phantom and to measure the effect of skin dose reduction by adding 1 cm-thick bolus. Method: The plan was compared with measurements using an adult anthropomorphic phantom combined with radiochromic films and thermoluminescent dosimeters. We also measured the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantom. Results: We found that 1 cm-thick bolus reduced the skin dose by up to 20% both in measurements and calculations. The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin (without breast attachment) doses. Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. Skin dose measurements using anthropomorphic phantom may be helpful to evaluate more realistic skin dose and the bolus effect in the magnetic field.

The front-end electronics design of dose monitors for beam delivery system of Shanghai Advanced Proton Therapy Facility

A front-end electronics of dose monitor has been developed for measuring irradiation dose to the patient in Shanghai Advanced Proton Therapy Facility.The parallel plate ionization chamber is used for the dose monitoring.Unlike the traditional method of recycling capacitor integration and voltage-to-frequency conversion,this dose monitor electronics uses the trans-impedance amplifier and analog-to-digital conversion method.It performs satisfactorily,with the integral nonlinearity of less than ±0.04 nA in the range of-400 to 50 nA and the resolution of about±0.6 nA.

Commissioning and Optimization of a Total Skin Electron Therapy Technique Using a High Dose Rate Electron Facility

Total skin electron therapy (TSET) is used for the treatment of Mycosis Fungoides. Several tech-niques have been developed, in order to achieve homogeneous dose distribution over the complete body surface. To implement a TSET technique, one has to optimize a variety of parameters. Monte Carlo simulation of TSET can facilitate this optimization. The aim of this study was to commission and optimize a TSET technique using the 4 and 6 MeV electron and the high dose rate facility on the Elekta Precise accelerator. The EGS4nrc/BEAMnrc Monte Carlo code was used. The beam data were calculated and measured at two different scoring planes for a single beam. The Model was validated by comparing the simulation with measurements. Two different vertical angles were used to obtain a uniform dose. The angle was optimized for best dose uniformity. The Rando phantom is placed on a rotating platform and rotates 60 degrees apart to facilitate the six patient position orientations. The doses delivered in a phantom by complete treatment were measured with Kodak EDR2 films and TLDs. The dose distribution varied among various scanning directions by 2 - 3 mm and 3 - 4 mm for 4 and 6 MeV respectively. The composite percentage depth dose of all six dual fields for the 4 and 6 MeV yielded an R80 of ~4 mm and ~6 mm, respectively. Dose uniformity was ±6% for 4 MeV and ±5% for 6 MeV. The bremsstrahlung contamination was 0.9% - 1.3%. Good agreements were found with published literature and inline with international protocols.

Dose Distributions in Simulated Electron Radiotherapy with Intraoral Cones Using Treatment Planning System

Aim: This study aims to evaluate the difference between depth data from an intraoral cone and a conventional irradiation tube calculated using a treatment planning system (TPS), and that measured using an intraoral cone for electron radiotherapy. Background: A TPS is only compatible with conventional irradiation tubes. However, such systems are not suitable for determining dose distributions when a special cone is employed. Materials and Methods: Dose distributions were calculated using the beam data for mounted intraoral cones using a TPS. Then, the dose distribution by field size was calculated for a low-melting-point lead alloy using the beam data for a mounted conventional tube. The calculated data were evaluated against the measured intraoral-cone depth data based on the dose and depth differences. Results: The calculated data for the intraoral cone case did not match the measured data. However, the depth data obtained considering the field size determined for the lead alloy using the conventional tube were close to the measured values for the intraoral cone case. The difference in the depth at which the absorbed dose was 50% of the maximum value of the percentage depth dose was less than ±4 mm for the generalized Gaussian pencil beam convolution algorithm and less than ±1 mm for the electron Monte Carlo algorithm. Conclusion: It was found that the measured and calculated dose distributions were in agreement, especially when then electron Monte Carlo algorithm was used. Thus, the TPS can be employed to determine dose distributions for intraoral cone applications.

Comparison of Calculated Fit and Experimental Calculations of Average Dose Deposited in Aluminum by High Energy Electron Beams

This paper presents the formalism for absorbed dose determination to Aluminum in high-energy electron beams using Rhodotron accelerator. Depth dose curve for Aluminum at electron energy of 10 MeV was calculated. The calculated curve in the model as a function of the depth is compared to the experimental. The agreement of the final results remained well within the expected acceptable range. The calculated values of dose-to-Aluminum are completely fit with the measured values in the range of 0.07% for electron energy of 10 MeV.

Radiation dose enhancement in skin therapy with nanoparticle addition: A Monte Carlo study on kilovoltage photon and megavoltage electron beams

AIM To investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage(k V) photon and megavoltage(MV) electron beams. Monte Carlo simulations were used to predict the dose enhancement when different types and concentrations of nanoparticles were added to skin target layers of varying thickness.METHODS Clinical k V photon beams(105 and 220 k Vp) and MV electron beams(4 and 6 MeV), produced by a Gulmay D3225 orthovoltage unit and a Varian 21 EX linear accelerator, were simulated using the EGSnrc Monte Carlo code. Doses at skin target layers with thicknesses ranging from 0.5 to 5 mm for the photon beams and 0.5 to 10 mm for the electron beams were determined. The skin target layer was added with the Au, Pt, I, Ag and Fe2O3 nanoparticles with concentrations ranging from 3 to 40 mg/m L. The dose enhancement ratio(DER), defined as the dose at the target layer with nanoparticle addition divided by the dose at the layer without nanoparticle addition, was calculated for each nanoparticle type, nanoparticle concentration and target layer thickness.RESULTS It was found that among all nanoparticles, Au had thehighest DER(5.2-6.3) when irradiated with kV photon beams. Dependence of the DER on the target layer thickness was not significant for the 220 k Vp photon beam but it was for 105 kV p beam for Au nanoparticle concentrations higher than 18 mg/m L. For other nanoparticles, the DER was dependent on the atomic number of the nanoparticle and energy spectrum of the photon beams. All nanoparticles showed an increase of DER with nanoparticle concentration during the photon beam irradiations regardless of thickness. For electron beams, the Au nanoparticles were found to have the highest DER(1.01-1.08) when the beam energy was equal to 4 MeV, but this was drastically lower than the DER values found using photon beams. The DER was also found affected by the depth of maximum dose of the electron beam and target thickness. For other nanoparticles with lower atomic number, DERs in the range of 0.99-1.02 were found using the 4 and 6 MeV electron beams.CONCLUSION In nanoparticle-enhanced skin therapy, Au nanoparticle addition can achieve the highest dose enhancement with 105 k Vp photon beams. Electron beams, while popular for skin therapy, did not produce as high dose enhancements as k V photon beams. Additionally, the DER is dependent on nanoparticle type, nanoparticle concentration, skin target thickness and energies of the photon and electron beams.

Dose inter-comparison studies for ^(60)Co gamma-ray and electron beam irradiation in the year 2002

Dose inter-comparison studies for Co γ-ray and 10 MeV electron beam irradiation were carried out 60 from July to October in 2002. The purpose of the studies was to check the reliability of the alanine-PE film dosime- ters made by CIAE, which will be used as transfer standard dosimetry system mainly for electron beam irradiation. The expanded uncertainty of CIAE alanine/EPR dosimetry system was 4.1% for doses not higher than 10 kGy and 5.4% for those above 10 kGy (k=2). CIAE alanine-PE film dosimeters were sent to JAERI, RISO (National Labora- tory in Denmark) and INCT respectively, which were irradiated by Co gamma-rays or electron beams in each labo- 60 ratory. The irradiated dosimeters were then sent back to CIAE for electron paramagnetic resonance (EPR) analysis. The agreements were obtained to be ±1.9% for gamma-ray dose measurement and ±4.3% for electron beam dose measurement, which were all within the combined uncertainty of the reference and CIAE alanine/EPR dosimetry system. Furthermore, the overall mean ratio was found to be 0.995 with 1.8% in the coefficient of variation (CV). The preliminary inter-comparison studies indicated that CIAE film alanine/EPR dosimetry system had the potential to be used as a transfer dosimetry system for high dose measurement.

多种水等效材料的医用电子束修正因子研究

针对水等效材料在医用电子束剂量测量中修正因子的测量和使用问题,通过扫描医用电子束在水中和水等效材料中的百分深度剂量(percentage depth dose,PDD)曲线,计算获得深度缩放因子c_(pl)、注量缩放因子h_(pl)及总修正因子k_(pl)的实验值。结果表明,通过c_(pl)和h_(pl)组合或仅使用k_(pl)均可将水等效材料测量结果转换为水吸收剂量。比较PDD曲线表明,在10~20 MeV电子能量下3种水等效材料通过c_(pl)-h_(pl)修正后的R_(50),较水中测量最大偏差分别为0.19%、0.28%、0.22%;经k_(pl)修正得到的R_(50),较水中测量最大偏差分别为0.23%、0.29%、0.18%。结论:研究提供了多种材料c_(pl)-h_(pl)、k_(pl)的实验值,可方便用户快速完成电子束水吸收剂量的测量,相比于c_(pl)-h_(pl),使用k_(pl)更加简单高效。

高能电子束辐照脆肉鲩鱼片的贮藏品质分析

该试验研究了高能电子束辐照技术应用于脆肉鲩鱼片的保鲜效果,采用不同剂量(0、1、3、5、7 kGy)的电子束辐照,结合真空包装于4℃冷藏条件下保鲜,测定菌落总数(APC)、脂质氧化产物(TBARs)、挥发性盐基氮(TVB-N)、质构(TPA)和色度,结合感官评价探究电子束辐照对鱼片冷藏期间贮藏品质的影响。结果表明,辐照能较大程度抑制鲩鱼片中微生物的增长,3~7 kGy的辐照剂量能使鲩鱼片在整个贮藏期间菌落总数保持在106 CFU/g以下,推断3 kGy是脆肉鲩鱼片最低有效剂量。虽然辐照处理后会导致鲩鱼片TBARs值增加,但在贮藏后期有延缓TBARs值上升的效果,5 kGy及更低剂量可维持鲩鱼片TBARs在较低水平。同样,辐照能延缓鱼片TVB-N含量的增加。辐照对鲩鱼片气味、质构和色值影响差异不显著。综合考量,在真空包装,4℃冷藏的条件下,3 kGy是脆肉鲩鱼片最低有效剂量,5 kGy是最高耐受剂量,使用3~5 kGy剂量电子束辐照处理,最适用于脆肉鲩生鱼片的贮藏保鲜。该研究结果为电子束辐照应用于脆肉鲩鱼片的保鲜提供参考依据。

心房颤动患者导管消融术不同管电流CT扫描方案对患者辐射剂量影响研究

目的研究心房颤动患者导管消融术不同管电流电子计算机断层扫描(CT)扫描方案对患者辐射剂量的影响。方法回顾性分析2020年7月至2022年11月于我院进行导管消融术治疗的133例心房颤动患者临床资料,根据患者胸部CT扫描管电流水平将其分为微管电流组(管电流为30mAs)、低管电流组(管电流为50mAs)、中管电流组(管电流为100mAs)和高管电流组(管电流为200mAs),四组例数分别为30例、37例、34例、32例。记录四组患者辐射剂量[CT剂量指数(CTDI)、CT剂量长度乘积(DLP)、有效辐射剂量(ED)]、客观图像质量[CT值、对比噪声比(CNR)、信噪比(SNR)]、主观图像质量[解剖结构显示、噪声、图像清晰度]、左心房(LA)直径、LA憩室显示率、肺静脉(PV)解剖变异显示率。结果四组辐射剂量比较差异有统计学意义(P<0.05),其中微管电流组CTDI、DLP、ED均低于低、中、高管电流组(P<0.05),低管电流组CTDI、DLP、ED均低于中、高管电流组(P<0.05),中管电流组CTDI、DLP、ED均低于高管电流组(P<0.05)。微管电流组LA、左上肺静脉(LSPV)及右上肺静脉(RSPV)的CT值、SNR、CNR均低于低、中、高管电流组(P<0.05),低、中、高管电流组LA、LSPV及RSPV的CT值、SNR、CNR比较差异均无统计学意义(P>0.05)。微管电流组解剖结构显示、噪声及图像清晰度评分均低于低、中、高管电流组(P<0.05),低、中、高管电流组解剖结构显示、噪声及图像清晰度比较差异均无统计学意义(P>0.05)。微管电流组LA直径、LA憩室显示率及PV解剖变异显示率均低于其他三组(P<0.05),低、中、高管电流组LA直径、LA憩室显示率及PV解剖变异显示率比较差异均无统计学意义(P>0.05)。结论与100mAs、200mAs管电流相比,心房颤动患者导管消融术采用50mAs管电流CT扫描辐射剂量明显较少,所获图像质量也能够达到相关标准。

电子直线加速器辐射环境监测与评价

以医用放射治疗、货物/车辆安全检查、工业辐照3类电子直线加速器作为研究对象,通过辐射环境剂量率监测,掌握不同类型加速器周围和不同关注点位的辐射环境状况,对监测数据做单因素方差分析和Bonferroni相关性分析。结果表明,虽然3类电子直线加速器的辐射环境监测剂量率数据均低于相关标准限值,但安全检查类电子直线加速器出入口及其侧防护墙位置与其他类关注点位的周围剂量当量率水平有显著差异。

TEPC及其中子剂量测量应用研究进展

基于组织等效正比计数器(Tissue-Equivalent Proportional Counter,TEPC)的辐射监测装置在中子周围剂量当量测量领域展现出独特优势和应用潜力,成为各国新型中子剂量测量技术的研究热点。本文阐述了TEPC基本工作原理、各种技术路线的工作机理和特点优势,综述了基于TEPC的中子周围剂量当量测量技术的国内外研究和应用现状,并对关键技术的未来发展进行了展望。

医用电子束水吸收剂量测量及其不确定度讨论

目前医用电子束水吸收剂量测量不确定度超过3%,很难满足临床治疗和医用电子加速器辐射源检定规程的要求。中国计量科学研究院采用水量热法开展了电子束辐射剂量学的研究,实现了电子束水吸收剂量绝对测量相对标准不确定度为0.35%,同时也开展了医用电子束的同质溯源工作,总结了电子束水吸收剂量测量的5个方案,相对标准不确定度包含最高的3.7%和最低的1.4%。为方便临床电子束水吸收剂量测量,给出了电离室剂量计选取、送检和使用不同校准系数的注意事项。

GENERAL PROPERTIES OF DOMESTIC RADIOCHROMIC FILM ELECTRON DOSIMETER

The project established a system for routine measurement of electron dose and brought about a complete experimental approach for high-dose dosimetry. The paper reports some general properties of domestic radiochromic pararosaniline cyanide (PR-CN) dye with polyvinyl butyral (PVB)-based film used for measuring electron dose. The optical absorption spectrum, the change in optical density as a function of thickness, distribution of the background optical density and spread of response, long-term stability, linear relationship between the change in optical density per unit thickness and absorbed dose, the minimum detectable limit, effect of environmental factors on background and response after irradiation, effect of light-exposition and the time of establishing complete response have been experimentally investigated.

Comparative Study on the Surface Dose of Some Bolus Materials

In order to investigate the possibility of using different materials as bolus in radiotherapy, five samples denoted by S2 - S6 were prepared and analyzed by comparison with one available commercial bolus denoted by S1. Sample S1 was a thermoplastic material from Qfix;S2 was a moldable silicon rubber (RTV-530 from Prochima);S3 and S4 were obtained by adding micrometric particles of Al and Cu respectively (at the same mass concentration of 5.5%);S5 was another moldable silicon rubber (GSP400 from Prochima) and S6 was a mixture of GSP400 and micrometric particles of Cu (at the mass concentration of 5.5%). The measurements of normalized transmitted dose as a function of sample thickness were performed for all samples (S1 - S6) at two values of electron beam energy (6 and 9 MeV) produced by a linear accelerator VARIAN 2100SC. The results showed that the maximum of the normalized transmitted dose of manufactured samples (S2 - S6) is registered at smaller sample thicknesses than for the analyzed commercial bolus (sample S1). The smallest sample thickness corresponding to normalized maximum point dose is obtained for sample S2 (RTV-530). Measurements performed for electron beam energy of 6 and 9 MeV have proven the possibility of using the manufactured samples as bolus in radiotherapy.

电子束辐照对新疆干果品质的影响及其最高耐受剂量的确定

目的 探究电子束辐照对4种新疆干果品质的影响,确定干果辐照工艺的最高耐受剂量。方法 采用0、2、4、6、8和10 kGy不同剂量电子束处理枸杞干、红枣干、无花果干、小白杏干,研究不同辐照剂量对水分、维生素C、总酸、总糖4种理化指标及色度、外观、风味、色泽和口感等5种感官品质的影响。结果 仅8 kGy辐照处理对枸杞干口感指标有不良影响,其他3种干果的感官指标几乎不受辐照处理的影响;10 kGy以内的辐照处理对红枣干的品质无不良影响;无花果干的总酸含量在辐照剂量>6kGy时有所上升,维生素C含量在10 kGy处理时显著低于对照;辐照剂量≥6 kGy时,小白杏干维生素C含量显著降低。结论 通过对电子束辐照新疆干果的品质影响及最高耐受辐照剂量的研究,确定枸杞干、红枣干、无花果干和小白杏干的最高耐受剂量分别是8、10、6和6 kGy。为电子束辐照在新疆干果灭菌工艺中的应用提供了理论基础。

CT值-电子密度转换曲线对VMAT计划剂量计算的影响

目的分析CT值-电子密度转换曲线对容积旋转调强放疗(Volumetric Modulated Arc Therapy,VMAT)计划剂量计算的影响。方法采集、建立不同管电压、管电流、扫描部位的9条CT值-电子密度转换曲线(H_100、H_120、H_140、C_100、C_120、C_140、A_100、A_120、A_140),并以头部扫描序列H_120条件为标准扫描条件,分别对同一鼻咽癌VMAT放疗计划进行剂量计算,将VMAT计划移植到验证模体,行剂量计算,创建验证计划,分析标准条件与非标准条件下的剂量差异。结果VMAT计划标准条件与非标准条件剂量对比,脑干剂量误差最大,Dmax误差为26.90 cGy,相对误差为0.52%;腹部条件A_140(腹部140 kV 300 mA)下与标准条件剂量学差异无统计学意义(P>0.05);其他条件下均与标准条件剂量学差异有统计学意义(P<0.05)。模体验证计划标准条件与非标准条件剂量对比,密质骨Dmean误差最大,为0.30 cGy,相对误差为0.56%;统计分析结果显示,模体验证放疗计划非标准条件与标准条件剂量比较,差异均有统计学意义(P<0.05)。结论不同CT值-电子密度转换曲线对VMAT计划剂量计算均有一定程度的影响;在临床工作中,必须针对不同的管电压、管电流、扫描部位等,建立标准的CT值-电子密度转换曲线;CT模拟定位和剂量计算时,应选择相应的扫描参数条件和CT值-电子密度转换曲线,以提高剂量计算的准确性。

低剂量电子显微表征下的出射波重构技术

原子级分辨率的成像表征对探究材料结构与性质间的联系具有重大意义。应用像差校正的高分辨电子显微成像技术(high⁃resolution transmission electron microscopy,HRTEM)可以实现亚埃尺度分辨率的图像表征,但电子束辐照敏感材料受限于辐照引起的结构损伤,无法用常规辐照剂量进行HRTEM成像表征。将出射波重构(exit wave reconstruction,EWR)技术应用于辐照敏感材料,一方面可以解决HRTEM图像中衬度反转的问题并提高图像分辨率至信息极限;另一方面,通过算法实现对信息的充分利用,适合于从低剂量数据中提取有效信息。采用低剂量EWR技术可以实现电子束敏感材料的原子级分辨率图像,为研究电子束辐照敏感材料提供更多可能性,也使针对出射波重构技术的研究具有更大的应用前景与科学意义。

医用电子加速器剂量校准及电离室有效测量点对剂量校准准确性的影响

目的为保障医用电子加速器输出剂量的准确性,对医用电子加速器进行剂量校准,并验证电离室有效测量点对剂量校准准确性的影响。方法依据JJG 589-2008《医用电子加速器辐射源检定规程》,在考虑及不考虑电离室有效测量点影响两种情况下,对医用电子加速器X线(6、10 MV)和电子线(6、8、12、15 MeV)进行剂量校准测量,分析测量结果,并进行验证。结果各能量挡的实测值与剂量指示值的偏差均符合JJG 589-2008中剂量偏差限值(±3%)的要求。在进行剂量校准时,若不考虑电离室有效测量点,对X线和电子线的剂量测量结果均有不同程度的影响,部分能量挡的剂量测量偏差接近于1%。结论电离室有效测量点对医用电子加速器剂量校准结果的影响不容忽视。从事剂量校准的工程师应严格依据JJG 589-2008的要求校准,确保剂量校准的准确性。